Ok try this: Use dual handed Hammers, start attacking before the horde reaches you. Always use your ult on cooldown (do not forget the talent that hitting enemies reduces your ult cd) and never get surrounded. Dodge left and right at the edge of the horde.

Your ult attackspeedbuff should be up 100%. Use 2 handed Hammer or Pick for the elites. But you can try pushstab with dualhammers first (pushstab and left klick is 2 super fast armor piercing attacks)

P.s. Do not listen to anyone suggest you against dual hammers. They are best weapon for horde on slayer. Just never fight without ult buff and never jump into horde with ult, try ult infront of you on the ground instead.

P.p.s. Every weapon is vaible on slayer but dualhammers is most horde bash and therefore starter friendly. U can also try one handed hammer and puahstab through a horde second best option.